材料科学基础清华skja.pptVIP

材料科学基础Fundamental of Materials §3.1 Basic concepts of alloys Ⅰ.Definition An alloy is the combination of metal(s) with other elements through chemical bonding. Ⅱ.Terminology 1. Component (or constituent) one component system two component system binary system three component system ternary system four component system quarternary system five component system quinary system 2. Composition It can be expressed either by atomic percentage (mol fraction) Xa or by mass percentage Xm 3. Phase A phase is a homogeneous part of the material in which no abrupt change in composition, structure and properties occurs. An alloy may be single phase or multi-phase material. 4. Structure Structure is a general term for the combination of atom arrangement including the types amounts and distribution of all types of material as well as grain size, defect etc. Ⅲ. Classification of Alloy Phases 1. According to structure Solid Solution Compound In Solid Solution, atoms of different component share a common lattice in variable proportion. 2. According to position of the alloy in phase diagram §3.2 Factors Affecting the Structure of Alloy Phase 1. What is size factor metallic radii rA+rB =d ionic radii r++r - =d covalent radii single bond radius Van der Waals radii CN radii 2. What is Electrochemical factor —— Electronegativity X X represents the ability of an atom of an element in the compond to attract electrons to itself. EAA—— bonding energy between A-A atoms EBB—— bonding energy between B-B atoms EAB—— bonding energy between A-B atoms 3. Electron concentration ( e/a ) Electron concentration ( e/a ) is the number of valence electrons per atom on the average. i.g